1. Field of the Invention
The present invention relates to a method for boring a wheel spoke rim. The invention also relates to a rim obtained using the method. The invention is also related to a spoke, a spoke nipple provided to equip the rim obtained by the method, as well as a wheel obtained by assembling the rim with such spokes and spoke nipples.
2. Background and Material Information
In a known manner, a wheel, especially a bicycle wheel, includes a central hub connected to a circular rim by two rows of spokes. The rim is formed of two circular bridges connected by two lateral flanks so as to form a box. The lateral flanks are extended outwardly by two wings, so as to form, with the upper bridge, an annular channel provided to receive a tubular. For certain rims that are provided to receive a tube, the channel is a mere groove formed by a caving-in of the upper bridge. The spokes are connected to the rim by nipples screwed at the end of the spokes. These nipples further make it possible to adjust the tension of the spokes.
To receive the spoke nipples in a conventional manner, the two bridges of the rim are bored with openings spread along the circumference of the rim. The openings of the lower bridge are provided to serve as a seat for the nipple heads. The openings of the upper bridge, with a greater diameter, are provided to enable the positioning of the spoke nipple from the outside.
To improve the conditions in which the nipple head takes support against the rim, and the distribution, in the rim, of the stresses induced by the tension of the spokes, it is known to equip the rims with eyelets that extend through the openings of the lower bridge. These eyelets are assembled by crimping to the periphery of the opening of the lower bridge. They further have a cup-shaped eyelet body whose lower portion rests on the lower bridge, and the upper portion has an edge that rests against the upper bridge. The base of these eyelets is bored for the passage of the nipple body. These eyelets are advantageous because they establish mechanical linkages between the two bridges, which reinforces the structure of the rim and its bending strength.
A monoblock eyelet is described in the patent application EP 130 449. These eyelets also exist in the form of two distinct elements assembled at the level of the crimping.
However, for such rims, the openings of the bridges constitute local weakening zones which weaken each of the two bridges. In addition, these openings must have a relatively large size. The openings of the lower bridge must indeed have a diameter that is sufficient to allow for the passage of the nipple body and its free rotation. The openings of the upper bridge must enable the passage of the nipple head upon which the fastening of the spoke to the rim, as well as the adjustment tools are dependent.
Another problem of these rims is that when adjusting the tension of the spokes, the spoke itself is torsionally biased and twists over itself before a relative movement occurs at the level of the threads for linking with the nipple. As a result, the tension adjustment of the spokes is relatively inaccurate, and the spokes do not work properly.
Another problem of these rims comes from the manufacturing of the eyelets. Indeed, if one wishes to equip the rim with cup-shaped double eyelets, the distance between the two bridges of the rim is directly related to the height of the cup of the eyelet. Since the eyelet is conventionally made of stainless steel by stamping, the maximum height of an eyelet is thereby limited, which imposes dimensional constraints for the rim.
However, a rim having threaded openings is known from the published Patent Application No. WO 93/09963. The threaded end of the spokes is connected to this rim by means of a nipple that is threaded internally and externally with a different pitch. This rim further has an unpunched upper bridge, except for the mounting of a valve, if necessary, which makes the rim airtight, and therefore appropriate for the mounting of a tubeless type of tire.
However, the lower bridge that is bored and threaded must be reinforced in its thickness to withstand the stresses, which results in an undesired increase in the weight and inertia of the rim. The mode for mounting the spokes does not solve the spoke twisting problem either.
An object of the invention is to propose a method for boring a rim which makes it possible to obtain a rim having improved mechanical characteristics, without any significant weight increase.
Another object of the invention is to propose a rim bored with openings which has an improved resistance to fracture.
Another object of the invention is to propose a rim in which the distance between the two bridges is freed from the height limit constraint for the cups of the eyelets.
Another object of the invention is to propose a wheel equipped with spokes whose tractional working conditions are improved.
Other objects and advantages of the invention will become apparent along the description that follows.
According to the invention, the method for making a rim bored with openings provided to receive spokes for linkage with a hub, the rim having a box with an upper bridge and a lower bridge, includes the feature that at least the lower bridge is bored with a through hole by means of flow drilling bit operating in the direction of the upper bridge.
The rim obtained using the method includes the feature that at least one of the bridges has a plurality of through holes demarcated by a backflow chimney whose height is greater than the thickness of the bridge.
The spoke provided to equip the preceding rim includes the feature that it has a joining piece affixedly assembled to the end of the spoke, and a tension adjusting screw mounted to rotate freely and set back with respect to the joining piece.
The wheel according to the invention has a rim such as aforementioned, a central hub and connecting spokes between the rim and the hub.
According to another characteristic, the rim includes at least one spoke such as aforementioned.